Hydraulic circuit with lockout valve in common return line



Sept. 29, 1964 J. A. JUNCK ETAL HYDRAULIC CIRCUIT WITH LOCKOUT VALVE INCOMMON RETURN LINE Filed Oct. 1, 1963 INVENTOR. JOHN A. JUNCK' BY ROGERA. R\C.E

FRANK H. wmmzns g 1 X A TORNEIYS United States Patent 3,150,568HYDRAULIC CIRCUIT WITH LOCKOUT VALVE IN COMMON RETURN LINE John A.Junck, Roger A. Rice, and Frank H. Winters, Joliet, Ill., assignors toCaterpillar Tractor Co., Peoria, 111., a corporation of California FiledOct. 1, 1963, Ser. No. 313,017 3 Claims. (Cl. 91-414) This inventionrelates to improvements in hydraulic circuits of the kind in which twoor more hydraulic motors or jacks are actuated by fluid under pressurefrom a single source and particularly to the type of circuit which hascome to be known as a common rail circuit because while separateconduits direct fluid to actuate the several jacks in one direction, asingle or common line serves to return fluid to the source as well as todirect fluid to any of the several jacks to actuate it in the oppositedirection.

Earthmoving scrapers now manufactured and sold by our assignee areprovided with common rail circuits for actuating double acting hydraulicjacks which adjust the bowl, the apron and the ejector of the scraper.Pressure of return fluid through the common line resulting fromoperation of one jack is communicated to the other jacks but does notactuate them because they are held against movement by hydrostaticpressure resulting from the particular positioning of their respectivecontrol valves. Difficulties have been experienced, however, because thebowl jacks sustain the weight of the heavily loaded bowl when it is in araised position by fluid locked in the smaller capacity or rod end ofthe jacks. Return pressure from the apron or ejector jacks is,therefore, communicated to the larger capacity or head ends of thejacks. This condition is further aggravated by the fact that lowering ofthe apron to its closed position is accompanied by a downward reactionon the bowl, sometimes creating peak pressures that are destructive tothe jacks and their associated linkages.

It is, therefore, the object of the present invention to provide acommon rail circuit of the kind described above with means to protectone jack or set of jacks against excessive pressures transmitted to itthrough the common rail.

A further and more specific object is to provide a lockout valve betweenthe common rail and jack to be protected, operable automatically whenthe jack is in a load sustaining condition, to prevent communication ofpressure from the common rail to the jack.

Further and more specific objects and the manner in which the inventionis carried into practice are made ap parent in the followingspecification wherein reference is made to the accompanying drawing.

The drawing is a schematic view of a common rail circuit with a singlesource of hydraulic fluid serving three jacks or sets of jacks shown forexample as jacks actuating the bowl, apron and ejector of an earthmovingscraper, those components of the circuit which are supported by thescraper and those which are supported by the tractor which draws thescraper being illustrated as separated by a broken line which intersectsthe view.

Generally speaking, the circuit disclosed in the drawing is the same asthat shown in our assignees copending application of Allyn J. Hein etal. for Hydraulic Circuits for Control of Earthmoving Scraper Bowls,Serial No. 247,056, now Patent No. 3,127,688. A brief description of theoperation of this circuit will facilitate an understanding of thepresent invention which forms a part thereof.

Referring to the drawing, a pump 35 is adapted to draw fluid from areservoir 36 and to direct it under pressure to the inlet port 37 of ascraper control valve 22. The

housing of this valve is bored for the reception of three slidable valvespools 16a, 18a and 20a for controlling the operation of three sets ofjacks, generally indicated at 16, 18 and 20, respectively, associatedwith the bowl, apron and ejector of a scraper.

The operation of the valve 22 is disclosed in detail in our assigneesPatent No. 3,068,596 and will be described herein only to the extentnecessary to an understanding of the present invention.

A pair of forked inlet passages 38 and 39 in the valve body communicatewith each other and with the first passage 37 so that with the valvespools in the neutral positions, as shown, fluid from the pump flowsconstantly through these passageways, thence to a discharge passage 40and back to the reservoir through a return line 41. A relief valve 42relieves excessive pressure on the discharge side of the pumpcommunicating it to the reservoir through the discharge line 41. Eachjack or set of jacks has what may be considered a high pressure and alow pressure end because the work or force required to move an implementpart in one direction, as when it is being raised or moving earth, isusually greater than that required to move it in the other direction.Movement of any one of the spools in the valve 22 to the right as viewedin the drawing communicates pressure to the high pressure end of itsassociated jack. For example, rightward movement of spool 16a admitsfluid under pressure to a line 4-6 and through line 45a to the rod endsof jacks 16 for raising the bowl. Similarly rightward movement of spool118 communicates pressure through a line 48 to the head end of jack isto actuate the apron. This pressure is communicated through a valvemechanism 64, the function and construction of which are set forth indetail in our assignees ccpending application of Allyn I. Hein et al.for Hydraulic Circuit for Tractor Drawn Scrapers and the Like, SerialNo. 154,790, now Patent No. 3,115,716. A detailed description of thisvalve, however, is unnecessary to an understanding of the presentinvention. Rightward movement of spool 20a admits fluid from inletpassage 39 through a line 50 to the head end of jack 20 for actuatingthe ejector. The opposite or low pressure ends of all of the jacks areconnected with a common manifold 52 in the control valve 22 whichcommunicates with each of the three valve spool bores and is opened byrightward movement of any spool into communication with a dischargemanifold 53 connected to the reservoir by the line 41. Consequentlyreturn fluid from any jack which has been pressurized by rightwardmovement of one of the spools is directed to the reservoir because thecommon manifold 52 is connected with the low pressure ends of the jacksby a common line 54 having a branch line 55 to the bowl jack, a branchline 56 to the ejector jack and a branch line 57 to the apron jack though the valve mechanism 54.

Moving of any of the jacks in the direction opposite to that describedabove is accomplished by movement of the corresponding spool in theopposite direction or to the left as viewed in the drawing whichcommunicates high pressure through the actuated spool to the manifold 52and thus to all of the jacks through line 54 and its branches 55, 56 and57. The valve spool which has been actuated also opens communication toa discharge passage 60 which is common to all of the spools and similarin configuration to the discharge passage 53. Passage 60 communicateswith passage 40 and return line 41 so that return fluid from theactuated jack is directed to the reservoir. It should be noted that theother jacks are not actuated by pressure in the common rail systembecause since their controlling spools remain in the neutral position,they provide no return to the reservoir and the jacks arehydrostatically locked.

A load check and quick drop valve assembly 66 is associated with thehead end of each of the bowl jacks 16 with the load check portion of thevalve functioning as described in the above mentioned Patent No.3,127,688 to contain the bowl supporting pressure in the rod end of thejack. A vent line 72 is associated with the valves 66 and the controlspool 16a in such a manner that when the spool is moved to a positioncommunicating pump 35 with the head end of jacks 16 through line 54 andbranch 55, the line 72 is placed in communication with the reservoirpermitting the load check valve to open so that fluid displaced from therod ends of the jacks may return to the reservoir.

With the system as above described and without the lockout valve,generally indicated at 110 and presently to be described in detail,pressure in the common rail system is communicated through the branch 55to the head end of jack 16 each time that the jacks 18 or 20 areactuated. It is this pressure added to the load which is being sustainedby the rod ends of the jacks 16 which presents the problems overcome bythe present invention.

The improvement over the circuit hereinabove described residesprincipally in the provision of the lockout valve, generally indicatedat 110, which prevents flow through the branch 55 of the common railcircuit when the bowl jacks 16 are sustaining a load, which condition isaccompanied by pressure in the line 72. The lockout valve includes aslidable spool 114 and a check valve 116. The spool 114 is biased by aspring 118 toward a position (not shown) which permits communicationbetween the valve inlet and outlet ports 129 and 122, respectively. Achamber 124- at the end of the spool 114 receives pressure through aline 126 communicating with line 72 so that when the spool 16a is in theneutral position shown, the load check pressure is communicated to thechamber 124 to overcome the force of spring 118 and hold the spool 114in the closed position shown. Consequently if either spool 180 or Zitais moved toward the left to create pressure in the common line 54,pressure cannot fiow through line 55 to the head end of the bowl jacks16. However when spool 16a is moved toward the left to effect loweringof the bowl, a groove 74 in the spool provides communication between thevent line 72 and a line 76 leading to the reservoir 36 to vent thepressure from the load check valves 66 and from chamber 124. The spool114 is moved to the right by the force of spring 118 augmented by thepressure in branch line 55 which enters the spring chamber through apassage 128 so that the pressure in branch line 55 is directed to thehead ends of jacks 16 to effect lowering of the bowl.

When spool 16a is returned to its neutral position, the vent line 72 isagain blocked and chamber 124 is again pressurized to move spool 114 toits closed position. When spool 16a is moved to the right to communicatepump pressure through the line 46 to the rod ends of jacks 16 to raisethe bowl, fluid displaced from the head end of the jacks is free toreturn to the reservoir through branch 55 since it opens the check valve116 in the valve assembly 110.

As has been described, pressure in vent line 72 is required topressurize the chamber 124 and hold spool 114 in its closed position.Under certain operating conditions, the pressure in common line 54, foractuation of motor 18 or 20, may exceed the pressure in jacks 16. Inorder to prevent this higher pressure, which is also present in thechamber of spring 118, from moving spool 114 to its open position,additional check valves 130 are provided to prevent displacement of oilfrom chamber 124 through the load check valve 66.

Lowering of the scraper bowl is necessary for emergency braking of thevehicle should the engine die during high-speed operation and sufficientair pressure is not available for operation of the brakes. Ability tolower the bowl when the engine is not running is also necessary as asafety measure during service of the machine, particularly the hydraulicmechanism which controls the bowl position. To permit such lowering ofthe bowl opening of the lockout valve without the aid of pressure isaccomplished by spring 118 when spool 16a is moved to the left to thelower position which vents the pressure from chamber 124 throughconduits 126, 72, groove 74 and conduit 76. As the weight of the bowlextends the pistons of jacks 16, the fluid displaced from the rod end ofthe jacks pressurizes the reservoir, thus forcing oil through thecollapsed vanes of pump 35, valve 22, common conduit 54, branch 55 andlock valve to the head ends of jacks 16 to fill the void created byextension of the pistons. This transfer of oil from the reservoir 36 tothe jacks 16 is also assisted by the vacuum created in the head end ofthe jacks upon their extension. This permits lowering of the scraperbowl when the engine and consequently pump 35 is not operating to supplyfluid to the head ends of the jacks.

We claim:

1. In a hydraulic circuit which includes a plurality of independentlyoperable reversible fluid motors, a source of fluid under pressure,means to direct fluid from said source to said motors, valve meansincluding a control element for each motor, separate conduits forcommunicating fluid from each control element to its respective motorfor driving the motor in one direction, and means including a singleconduit common to all of the motors for returning fluid through saidvalve means and for driving the motors in the opposite direction, theimprovement which comprises a lockout valve between said single conduitand one of said motors to prevent transfer of pressure from the singleconduit to said one motor upon actuation of the other motors.

2. The combination of claim 1 with means operable automatically to opensaid lockout valve when actuating pressure is directed to said onemotor.

3. The combination of claim 1 with means to open the lockout valve whenactuating pressure fails.

Tan Nov. 17, 1959 Hein et al Dec. 18, 1962

1. IN A HYDRAULIC CIRCUIT WHICH INCLUDES A PLURALITY OF INDEPENDENTLYOPERABLE REVERSIBLE FLUID MOTORS, A SOURCE OF FLUID UNDER PRESSURE,MEANS TO DIRECT FLUID FROM SAID SOURCE TO SAID MOTORS, VALVE MEANSINCLUDING A CONTROL ELEMENT FOR EACH MOTOR, SEPARATE CONDUITS FORCOMMUNICATING FLUID FROM EACH CONTROL ELEMENT TO ITS RESPECTIVE MOTORFOR DRIVING THE MOTOR IN ONE DIRECTION, AND MEANS INCLUDING A SINGLECONDUIT COMMON TO ALL OF THE MOTORS FOR RETURNING FLUID THROUGH SAIDVALVE MEANS AND FOR DRIVING THE MOTORS IN THE OPPOSITE DIRECTION, THEIMPROVEMENT WHICH COMPRISES A LOCKOUT VALVE BETWEEN SAID SINGLE CONDUITAND ONE OF SAID MOTORS TO PREVENT TRANSFER OF PRESSURE FROM THE SINGLECONDUIT TO SAID ONE MOTOR UPON ACTUATION OF THE OTHER MOTORS.